Uses laser illumination and a heterodyned laser interferometry video system to measure the deformations of the lid from an applied pressure change. Can measure sub-micron deformations across the entire image by measuring the phase relationship of the pure laser light that reflects from each package’s lid, and a change in the deformation of a package lid of more than a tenth of a wavelength of light can be accurately measured. Works well as a gross leak detector, no matter how gross the leak is.